Soft copper alloy, and soft copper wire or plate material

ABSTRACT

A method of fabricating soft copper alloy wire having flexure resistance and heat resistance, includes casting a molten alloy of a copper alloy including 10 mass ppm or less of oxygen, and 0.005 mass % to 0.6 mass % of indium, at a predetermined temperature, to provide a cast bar of the copper alloy having equiaxed crystal, rolling the cast bar of the copper alloy having equiaxed crystal to provide a rolled copper alloy, and conducting a cold drawing and annealing on the rolled copper alloy.

RELATED APPLICATIONS

The present Application is a Divisional Application of U.S. patent application Ser. No. 11/159,417, which was filed on Jun. 23, 2005.

The present application is based on Japanese patent application No. 2004-159183, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a soft copper alloy as conductive material, and a soft copper alloy wire or plate material.

2. Description of the Related Art

In modern science and technology, electricity is used in all parts including electric power as source of power and electrical signals, and to transmit electricity, conductors such as cables and leadwires are used. Materials for such conductors include copper, silver and other metals of high conductivity, and in particular copper wires are used most widely in consideration of cost and other aspects.

Copper may be roughly classified into hard copper and soft copper depending on its molecular arrangement, and various types of copper having desired properties are used depending on the application and purpose.

For example, in cables connected to driving parts of industrial robot or automatic machine tool, rigid and hard copper wire is not suited, and soft copper wire is used.

In lead wires for electronic components, hard copper wires are used, because, once connected, they are not detached and moved again, and it is desired to prevent deformation when connecting.

In any copper wire, additive-free copper is rarely used, and a proper amount of additive having a desired property is often added, and the molecular structure is also controlled.

For example, heat resistance or mechanical characteristic will be enhanced by adding indium or tin, as compared with pure copper, but if added too much, the conductivity may be lowered.

Or, as the oxygen content in copper increases, conductivity or cold workability may be lowered, or by forming an oxide by reaction with an additive, wire breakage is likely to occur when forming an ultrathin wire.

To solve these problems, so far, various methods have been proposed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2002-363668 and JP-A No. 9-256084).

However, much has not been studied yet about soft copper wires. For example, the invention disclosed in JP-A No. 2002-363668 is an invention about hard copper wire, and flexure resistance is not specifically evaluated, nothing is studied about soft copper wire which is superior in flexure resistance. Heat resistance is not evaluated either.

Although the invention of JP-A No. 9-256084 is an invention about soft copper alloy, the crystal grain size after annealing is specified to be 1.6 um or less. The manufacturing condition is very difficult to maintain the crystal grain size at this level, and although the properties are excellent, it is not practical to realize this because of too many economical loads.

The invention is devised in the light of above background, and it is hence an object thereof to provide a conductive material having both flexure resistance and heat resistance suitable to application into flexure-resistant conductive materials such as power distribution wires, vehicle wires and robot wires.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a conductive material having both flexure resistance and heat resistance suitable to application into flexure-resistant conductive materials such as power distribution wires, vehicle wires and robot wires.

According to one aspect of invention, a soft copper alloy comprises:

10 mass ppm or less of oxygen; and

more than 0.005 mass % and less than 0.6 mass % of indium.

The soft copper alloy may further comprising 0.0001 to 0.003 mass % of phosphorus.

The softer copper alloy may further comprise 0.001 to 0.1 mass % of boron.

The soft copper alloy may further comprise phosphorus and boron together in a range of 0.1 mass % or less.

It is preferred that a temperature of molten alloy in casting is 10 to 50 degrees higher than a melting point of the alloy so that a crystal structure in cast bar comprises an equiaxed crystal.

According to another aspect of the invention, provided is a soft copper alloy wire or plate material manufactured by processing the soft copper alloy, wherein an average crystal grain size after annealing is 2 to 20 um.

It is preferred that 0.2% proof strength is 130 MPa or more.

It is preferred that tin or Mg or Ag is included in a range of a conductivity not lower than 85% IACS.

It is preferred that a tensile strength after heating for 1 hour at 400° C. is within 4%.

Thus, according to the invention, a soft copper alloy wire suppressed in decline of conductivity and having excellent flexure resistance and heat resistance can be provided, and it is expected to extend the service life of conductive materials when used in flexure resistant conductive materials such as power distribution wires, vehicle wires or robot wires.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments according to the invention will be explained below referring to the drawings, wherein:

FIG. 1 is a metallographic cross-section view of crystal structure, showing a cast bar of columnar crystal and a cast bar of equiaxed crystal; and

FIG. 2 is a cross-section view comparing crystal structure between a copper alloy of the invention and a comparative material of pure copper.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Copper alloys in preferred embodiments of the invention are explained below.

[Quality of Cast Bar and Rough Drawn Wire]

Qualify of rough drawn wire obtained by continuous casting is determined by the state of texture of copper alloy in the cast bar before processing. Therefore, in order to manufacture an alloy wire of copper-indium system at a stable quality usable industrially, it is required to control the texture in a stage of cast bar.

Table 1 compares the state of texture and quality of rough drawn wires obtained from cast bars when cast bars were manufactured in several different conditions. Herein, the casting speed was 30 tons/h, and wires were cast and cooled by using a casting ring made of copper. Continuous casting and rolling was operated by SCR system.

In this embodiment, all wires were continuously cast and rolled by SCR system, but the invention is not limited to this system, may be realized by Hazley type continuous casting and rolling system or other manufacturing method.

TABLE 1 Contained Contained Element: Element: Molten copper alloy Sample oxygen Indium temperature (above Cast bar Quality of rough No. (mass ppm) (mass %) melting point (deg.) texture drawn wire 1 8 0.1 and 0.2 100 to 70 columnar X (too many crystal flaws to make product) 2 9 0.1 and 0.2 45 equiaxed ⊚ (excellent) crystal 3 7 0.1 and 0.2 30 equiaxed ⊚ (excellent) crystal 4 10 0.1 and 0.2 10 equiaxed ◯ (slight flaws) crystal 5 8 0.1 and 0.2 5 machine — (no product) stop

Generally, molten copper temperature when manufacturing copper or copper alloy is preferably said to be higher than the melting point by 50 degrees or more, but as known from the results in Table 1, rough drawn wires of favorable quality could be obtained at the molten copper alloy temperature higher than melting point by 10 degrees to 45 degrees only. Thus, even if the molten copper alloy temperature is not higher than the melting point by 50 degrees or more, it is known that favorable rough drawn wires can be obtained. However, if the molten copper alloy temperature was not higher than the melting point by 5 degrees or more, the machine stopped and products could not be obtained. In the cast bar when obtaining favorable rough drawn wires, the texture of copper alloy was equiaxed crystal. Hence, to obtain rough drawn wires of favorable quality, it is desired to use cast bars made of copper alloy having equiaxed crystal, and further to manufacture cast bars made of copper alloy having equiaxed crystal, it is preferred to set the molten copper temperature at 10 to 50 degrees higher than the melting point when casting. More preferably, the molten copper temperature should be set at 10 to 45 degrees higher than the melting point when casting.

In any example in Table 1, additives such as phosphorus and boron are not included, but in this copper-indium alloy system, similar effects could be obtained regardless of presence or absence of trace elements such as phosphorus and boron.

Comparative cross-section view of cast texture sections is shown in FIG. 1.

[Study on Conductivity of Copper Alloy Wire]

To determine favorable compositions in copper alloy of the invention, alloys of several different compositions were tested, and results are shown in Table 2.

TABLE 2 Oxygen Proof Sample In P B concentration Conductivity strength Crystal Heat Overall No. (mass %) (mass %) (mass %) (mass ppm) (% IACS) (Mpa) gain size resistance evaluation 1 0 7 101.5 102 X X X 2 0.005 8 100.8 122 X X X 3 0.01 9 100.2 140 ◯ ◯ ◯ 4 0.02 7 100 145 ◯ ◯ ◯ 5 0.05 7 99.5 148 ◯ ◯ ◯ 6 0.1 8 98 150 ◯ ◯ ⊚ 7 0.2 9 94 152 ◯ ◯ ⊚ 8 0.3 7 92 155 ◯ ◯ ⊚ 9 0.5 6 90 160 ◯ ◯ ◯ 10 0.6 8 85 162 ◯ ◯ ◯ 11 0.7 9 83 163 ◯ ◯ X 12 0.15 0.05 8 95 156 ◯ ◯ ◯ 13 0.3 0.0003 0.05 7 91 160 ◯ ◯ ◯ 14 0.1 0.0003 9 98 155 ◯ ◯ ◯

In Table 2, the crystal grain size was evaluated to be approved (o) when 20 um or less, and rejected (x) when exceeding 20 um. The heat resistance was approved (o) when the strength decline was within 4% after heating test for 1 hour at 400° C., and rejected (x) if exceeding this value. The overall evaluation was excellent (⊚), fair (∘) or poor (x).

Test results in Table 2 were obtained from rough drawn wires of 8 mm in diameter manufactured by SCR casting and rolling from cast bar obtained in the range of appropriate conditions in Table 1. The wires were further cold drawn to diameter of 1.2 mm. In the drawing process, the wires were electrically annealed in the condition of speed of 220 m/min and annealing voltage of 24 V or more.

In alloy wires not containing other additives than indium, properties were compared by different contents of indium.

Comparing samples 1 to 11, along with increase of indium content, the conductivity dropped and the proof strength of soft copper alloy wire was improved. Generally, in soft copper alloy wire, the conductivity is preferred to be 85% IACS or more, and according to this standard, sample 1 to sample 10 satisfied the standard, but sample 11 failed to satisfy. Considering from these results, in the copper alloy of the invention, a preferred indium content is 0.6 mass % at maximum.

Besides, 0.2% proof strength having effects on flexure life indicates values of 110 to 120 MPa generally in tempered pure copper (TPC), and each value of sample 2 to sample 11 exceeded the average value of pure copper.

Hence, sample 2 to sample 10 satisfy the standard as copper alloy of the invention from the viewpoint of conductivity and soft copper alloy wire proof strength, and the specified condition is the indium content of 0.005 to 0.6 mass %.

When the indium content is in the above range, favorable properties are shown, and this reason is as follows: in copper-indium system alloy, characteristics are improved as compared with copper alone because indium is present in the copper as solid solution element. When indium existing in copper as solid solution element increases, the mechanical properties of copper alloy can be improved, while the conductivity of copper alloy is lowered on the other hand.

Specifically, when the indium content is less than 0.005 mass %, characteristic improvement as solid solution element is not obtained, and hence indium content of 0.005 mass % or more is needed, but if the indium content is 0.6 mass % or more, the conductivity is lowered below the standard value.

Hence, the indium content of copper alloy wire in the invention is desired to be 0.005 to 0.6 mass %.

[Study on Oxygen Content of Copper Alloy Wire]

In continuous casting and rolling method, the amount of oxygen contained in copper alloy is preferred to be 10 mass ppm or less. The reason is, although the characteristics are improved in copper-indium system alloy more than in copper alone as mentioned above, that increase of oxygen content while indium is present as solid solution element in copper causes to form an oxide of indium, which does not contribute to improvement of characteristics.

In the copper alloy of the invention, the standard value of oxygen content is 10 mass ppm or less.

[Study on Crystal Grain Size of Copper Alloy Wire]

Crystal grain size varies with content of additives, and with manufacturing condition of alloy wire. The smaller the crystal grain size, the higher the mechanical property, especially the proof strength becomes. When the crystal grain size becomes 20 um or more, the proof strength is lowered, and it is not desired in the invention. Depending on the alloy composition or manufacturing condition, for example, the crystal grain size may be 20 um or more. On the other hand, if the crystal grain size is 2 um or more, excellent mechanical characteristics will be obtained, but the manufacturing condition is difficult for achieving this level, and it is not suited to mass production. Accordingly, in the invention, the crystal grain size of the copper alloy is specified in range of 2 to 20 um.

As shown in the evaluation of crystal grain size in Table 2, in the case the indium content in copper alloy is 0.005 mass % or less, the crystal grain size is 20 um or more and it is rejected, but when contained by 0.01 mass %, the crystal grain size is 20 um or less, and it is approved. Hence, in the copper alloy of the invention, a preferred indium content is 0.01 to 0.6 mass %.

FIG. 2 shows a crystal structure of sample 1 and sample 6 in Table 2. It is known that the product of the invention is small in crystal grain size and excellent in texture.

[Study on Heat Resistance of Copper Alloy Wire]

Heat resistance was studied. The evaluation standard of heat resistance in the copper alloy of the invention is that drop of strength should be within 4% after heating for 1 hour at 400° C.

Using the copper alloy of the invention, the strength after heating tests in various conditions was measured, and results are summarized in Table 3.

TABLE 3 Heating temperature (° C.) before the test 250 300 400 500 550 Strength (Mpa) after heating test (1 hour) (value in parentheses shows a ratio compared with strength before the test) Embodiment 248 248 248 249 250 253 Cu-0.1 mass % (1) (1) (1) (1.004) (1.008) (1.020) In Comparative 248 246 245 242 238 235 material pure (1) (0.991) (0.989) (0.976) (0.960) (0.948) copper (TPC) Strength (Mpa) after heating test (10 hours) (value in parentheses shows a ratio compared with strength before the test) Embodiment 248 246 246 246 246 246 Cu-0.1 mass % (1) (0.992) (0.992) (0.992) (0.992) (0.992) In Comparative 248 243 242 236 232 227 material pure (1) (0.980) (0.976) (0.952) (0.935) (0.915) copper (TPC)

The sample used in the heat resistance test was hardly changed in strength after heating for 1 hour at 400° C., and it was sufficiently approved. When temperature condition was changed after heating test, the strength was hardly changed, and the change was extremely small as compared with pure copper used as comparative example.

When the testing time was extended to 10 hours, the strength after heating test was hardly changed, and the copper alloy of the invention has been confirmed to have an excellent heat resistance.

As shown in the evaluation of heat resistance in Table 2, in the case the indium content in copper alloy is 0.005 mass % or less, the heat resistance did not satisfy the standard, but when contained by 0.01 mass %, the heat resistance satisfied the standard and was approved. Hence, in the copper alloy of the invention, the indium content is more preferably 0.01 to 0.6 mass %.

[Study on Concentration Range of Phosphorus and Boron in Copper Alloy Wire]

Other elements were added to copper-indium system alloy, and effects were studied.

Addition of boron to copper alloy was very useful for pulverization of crystal, having no effect of lowering the conductivity. As one of the embodiments of the copper alloy of the invention, sample 12 in Table 2 is shown as an example of adding boron.

The indium content of sample 12 is 0.15 mass %, and there is no comparative sample of same indium content, but when compared with sample 6 of indium content of 0.1 mass % and sample 7 of indium content of 0.2 mass %, the value of conductivity of sample 12 is an intermediate value of conductivity of sample 6 and sample 7, and it is known that the conductivity of copper alloy is not changed by addition of boron. On the other hand, the value of proof strength of sample 12 is higher than either value of proof strength of sample 6 and sample 7, and it is known that addition of boron contributes to enhancement of proof strength of copper alloy.

When the addition of boron is slight, sufficient pulverization effect of crystal is not obtained, but when too much boron is added, troubles are likely to occur at the time of casting. Hence, a proper range of addition of boron in the invention is 0.01 to 0.1 mass %.

Addition of phosphorus to copper alloy is effective in preventing blow holes and enhancing the equality of cast material, and is useful for improving the surface quality of rough drawn wire. As an embodiment of copper alloy of the invention, phosphorus is added in sample 14 shown in Table 2.

The indium content of sample 14 is 0.1 mass %, and when compared with comparative example of sample 6 having same indium content, the value of conductivity of sample 14 is same as conductivity of sample 6, and it is known that the conductivity of copper alloy is not changed by addition of phosphorus in sample 14. On the other hand, the value of proof strength of sample 14 is higher than the proof strength of sample 6, and it is known that addition of phosphorus contributes to enhancement of proof strength of copper alloy, and it seems to be due to effect of enhancing the quality of cast material.

To obtain such effect, phosphorus must be added by 0.0001 mass % or more, but at content of 0.003 mass %, the conductivity is lowered by about 2.2% as compared with additive-free sample. It is not desired to add phosphorus by 0.003 mass % or more because the conductivity is lowered. Hence, a standard range of addition of phosphorus in the copper alloy of the invention is 0.0001 to 0.003 mass %.

Both boron and phosphorus were added to copper alloy in sample 13 in Table 2.

The indium content of sample 13 is 0.3 mass %, and when compared with comparative example of sample 8 of same indium content, the value of conductivity of sample 13 is almost same as conductivity of sample 8, and the value of proof strength of sample 13 is higher than the proof strength of sample 8, and it is known that addition of both boron and phosphorus is known to contribute to enhancement of proof strength of copper alloy, without causing any particular adverse effect.

Summing up these results, an appropriate composition of copper alloy of the invention comprises an oxygen content of 10 mass ppm or less, and an indium content of 0.005 to 0.6 mass % in consideration of conductivity and proof strength, or 0.01 to 0.6 mass % in consideration of also crystal grain size and heat resistance. Boron and phosphorus are not always necessary, but when added, boron is desired to be added by 0.01 to 0.1 mass %, and phosphorus by 0.0001 to 0.003 mass %.

Other elements are known not to contribute to enhancement of properties of copper alloy, and are not particularly demanded. However, in the manufacturing field of copper alloy, entry of other elements may occur. Possible elements include tin, magnesium and silver. By entry of these elements, drop of mechanical characteristic is hardly possible, but the conductivity may be lowered. Accordingly, in a range of conductivity of copper alloy not becoming lower than 85% IACS, copper alloys including such elements, tin, magnesium or silver, are considered to be included in the scope of the invention.

[Study on Proof Strength of Copper Alloy Wire]

The copper alloy wire of the invention is required to have a long flexure life. In copper alloy wires differing in 0.2% proof strength, flexure life was measured, and results are shown in Table 4.

TABLE 4 0.2% proof Flexture life strength (distortion Flexture life ratio (as Sample (Mpa) 0.5%) compared to TPC at 1) Pure copper 110 5.012 1.0 (TPC) Cu-0.1 mass % In 131 7.523 1.5 (anneal 1) Cu-0.1 mass % In 159 12.012 2.4 (anneal 2) Cu-0.1 mass % In 182 15.009 3.0 (anneal 3) Cu-0.1 mass % In 199 18.112 3.6 (anneal 4)

The flexure life was measured by using copper alloy wire of 0.1 mm in diameter, in the condition of bending distortion of 0.5%, load of 32 g, and right and left 90-degree bending of 4 sec/way.

Proof strength of pure copper is generally about 100 to 120 MPa, and it was 110 MPa in pure copper used as comparative material in the present test. By contrast, in copper alloys of the invention, high values of proof strength were obtained although slightly different depending on annealing conditions, and the flexure life was also extended along with improvement of proof strength.

Comparing a sample with 0.2% proof strength of 131 MPa and a comparative example with proof strength of 110 MPa, the flexure life is increased to about 1.5 times, and this result is sufficient for the purpose of extending the flexure life. Hence, the desired value of 0.2% proof strength in the copper alloy wire of the invention is 130 MPa or more.

[Electric Annealer Condition]

As mentioned above, an electric annealer was used when drawing from a rough drawn wire in manufacture of copper alloy wire in the invention. A test was conducted to determine an appropriate electric annealer condition for the invention.

The speed was fixed at 220 m/min, and the annealing voltage of the electric annealer was varied, and in the obtained copper alloy wires, the tensile strength, 0.2% proof strength and elongation were measured, and results are shown in Table 5. These copper alloys are copper-0.1 mass % indium alloys.

TABLE 5 0.2% proof Anneal voltage Tensile strength (V) strength (Mpa) (Mpa) Elongation (%) 20 455 450 1.0 22 360 350 2.0 24 295 230 14 25 265 170 17 26 259 154 23 27 251 135 31 28 250 133 32 TPC 240 124 31 comparative material

Approval standard values were set at elongation of 10% or more and 0.2% proof strength of 125 MPa or more, and samples in an annealing voltage range of 24 V to 28 V satisfied the standard. At over 28 V, the experiment could not be conducted due to limit of the equipment.

This experiment was carried out by using an electric annealer excellent in productivity, but by traveling annealing by using a tubular electric furnace, it seems that copper alloy wires having more stable elongation and proof strength as compared with in the present test results will be obtained.

Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth. 

1. A method of fabricating soft copper alloy wire having flexure resistance and heat resistance, comprising: casting a molten alloy of a copper alloy comprising 10 mass ppm or less of oxygen, and 0.005 mass % to 0.6 mass % of indium, at a predetermined temperature, to provide a cast bar of the copper alloy having equiaxed crystal; rolling the cast bar of the copper alloy having equiaxed crystal to provide a rolled copper alloy; and conducting a cold drawing and annealing on the rolled copper alloy.
 2. The method for fabricating soft copper alloy wire having flexure resistance and heat resistance, according to claim 1, wherein a temperature of molten alloy in casting is 10° C. to 50° C. greater than a melting temperature of the copper alloy.
 3. The method for fabricating soft copper alloy wire having flexure resistance and heat resistance, according to claim 1, wherein the copper alloy further comprises 0.0001 mass % to 0.003 mass % of phosphorus.
 4. The method for fabricating soft copper alloy wire having flexure resistance and heat resistance, according to claim 1, wherein the copper alloy further comprises 0.01 mass % to 0.1 mass % of boron.
 5. The method for fabricating soft copper alloy wire having flexure resistance and heat resistance, according to claim 1, wherein the copper alloy includes phosphorus and boron together in a range of 0.1 mass % or less.
 6. The method for fabricating soft copper alloy wire having flexure resistance and heat resistance, according to claim 1, wherein the indium included in the copper alloy is 0.1 mass % to 0.2 mass %.
 7. The method of fabricating soft copper alloy wire having flexure resistance and heat resistance, according to claim 1, wherein the annealing is conducted after the cold drawing, wherein an average crystal gain size after annealing is in a range from 2 μm to 20 μm. 